using System;
using System.Threading;
using ServiceStack.Logging;
using ServiceStack.Redis;
using ServiceStack.Text;

namespace ServiceStack.Messaging.Redis;

internal class MessageHandlerWorker(
    IRedisClientsManager clientsManager,
    IMessageHandler messageHandler,
    string queueName,
    Action<MessageHandlerWorker, Exception> errorHandler)
    : IDisposable
{
    private static readonly ILog Log = LogManager.GetLogger(typeof(MessageHandlerWorker));

    readonly object msgLock = new();

    public string QueueName { get; set; } = queueName;

    private int status;
    public int Status => status;

    private Thread? bgThread;
    private int timesStarted = 0;
    private bool receivedNewMsgs = false;
    public Action<MessageHandlerWorker, Exception> errorHandler { get; set; } = errorHandler;

    private DateTime lastMsgProcessed;
    public DateTime LastMsgProcessed => lastMsgProcessed;

    private int totalMessagesProcessed;
    public int TotalMessagesProcessed => totalMessagesProcessed;

    private int msgNotificationsReceived;
    public int MsgNotificationsReceived => msgNotificationsReceived;

    public MessageHandlerWorker Clone()
    {
        return new MessageHandlerWorker(clientsManager, messageHandler, QueueName, errorHandler);
    }

    public void NotifyNewMessage()
    {
        Interlocked.Increment(ref msgNotificationsReceived);
            
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Started)
        {
            if (Monitor.TryEnter(msgLock))
            {
                Monitor.Pulse(msgLock);
                Monitor.Exit(msgLock);
            }
            else
            {
                receivedNewMsgs = true;
            }
        }
    }

    public void Start()
    {
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Started)
            return;
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Disposed)
            throw new ObjectDisposedException("MQ Host has been disposed");
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Stopping)
            KillBgThreadIfExists();

        if (Interlocked.CompareExchange(ref status, WorkerStatus.Starting, WorkerStatus.Stopped) == WorkerStatus.Stopped)
        {
            Log.Debug("Starting MQ Handler Worker: {0}...".Fmt(QueueName));

            //Should only be 1 thread past this point
            bgThread = new Thread(Run) {
                Name = "{0}: {1}".Fmt(GetType().Name, QueueName),
                IsBackground = true,
            };
            bgThread.Start();
        }
    }

    public void ForceRestart()
    {
        KillBgThreadIfExists();
        Start();
    }

    private void Run()
    {
        if (Interlocked.CompareExchange(ref status, WorkerStatus.Started, WorkerStatus.Starting) != WorkerStatus.Starting) return;
        timesStarted++;

        try
        {
            lock (msgLock)
            {
                while (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Started)
                {
                    receivedNewMsgs = false;

                    using (var mqClient = new RedisMessageQueueClient(clientsManager))
                    {
                        var msgsProcessedThisTime = messageHandler.ProcessQueue(mqClient, QueueName,
                            () => Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Started);
                            
                        totalMessagesProcessed += msgsProcessedThisTime;

                        if (msgsProcessedThisTime > 0)
                            lastMsgProcessed = DateTime.UtcNow;
                    }

                    if (!receivedNewMsgs) 
                        Monitor.Wait(msgLock);
                }
            }
        }
        catch (Exception ex)
        {
#if !NETCORE
                //Ignore handling rare, but expected exceptions from KillBgThreadIfExists()
                if (ex is ThreadInterruptedException || ex is ThreadAbortException)
                {
                    Log.Warn("Received {0} in Worker: {1}".Fmt(ex.GetType().Name, QueueName));
                    return;
                }
#endif

            Stop();
            errorHandler?.Invoke(this, ex);
        }
        finally
        {
            //If it's in an invalid state, Dispose() this worker.
            if (Interlocked.CompareExchange(ref status, WorkerStatus.Stopped, WorkerStatus.Stopping) != WorkerStatus.Stopping)
            {
                Dispose();
            }
        }
    }

    public void Stop()
    {
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Disposed)
            return;

        if (Interlocked.CompareExchange(ref status, WorkerStatus.Stopping, WorkerStatus.Started) == WorkerStatus.Started)
        {
            Log.Debug("Stopping MQ Handler Worker: {0}...".Fmt(QueueName));
            Thread.Sleep(100);
            lock (msgLock)
            {
                Monitor.Pulse(msgLock);
            }
        }
    }

    private void KillBgThreadIfExists()
    {
        try
        {
            if (bgThread is { IsAlive: true })
            {
                //give it a small chance to die gracefully
                if (!bgThread.Join(500))
                {
                    //Ideally we shouldn't get here, but lets try our hardest to clean it up
                    Log.Warn("Interrupting previous Background Worker: " + bgThread.Name);
                    bgThread.Interrupt();
                    if (!bgThread.Join(TimeSpan.FromSeconds(3)))
                    {
                        Log.Warn(bgThread.Name + " just wont die, so we're now aborting it...");
#pragma warning disable CS0618, SYSLIB0014, SYSLIB0006
                        bgThread.Abort();
#pragma warning restore CS0618, SYSLIB0014, SYSLIB0006
                    }
                }
            }
        }
        finally
        {
            bgThread = null;
            status = WorkerStatus.Stopped;
        }
    }

    public virtual void Dispose()
    {
        if (Interlocked.CompareExchange(ref status, 0, 0) == WorkerStatus.Disposed)
            return;

        Stop();

        if (Interlocked.CompareExchange(ref status, WorkerStatus.Disposed, WorkerStatus.Stopped) != WorkerStatus.Stopped)
            Interlocked.CompareExchange(ref status, WorkerStatus.Disposed, WorkerStatus.Stopping);

        try
        {
            KillBgThreadIfExists();
        }
        catch (Exception ex)
        {
            Log.Error("Error Disposing MessageHandlerWorker for: " + QueueName, ex);
        }
    }

    public IMessageHandlerStats GetStats()
    {
        return messageHandler.GetStats();
    }

    public string GetStatus()
    {
        return $"[Worker: {QueueName}, Status: {WorkerStatus.ToString(status)}, ThreadStatus: {bgThread.ThreadState}, LastMsgAt: {LastMsgProcessed}]";
    }
}